It is known that a photographic image having ultra-high contrast can be formed using a certain silver halide, and such a technique is used in the field of photographic printing plate making.
For example, it is known that a line image or a dot image having high contrast and high blackening density in which the image area and non-image area can be clearly distinguished can be obtained by developing a lith film with a silver chlorobromide emulsion containing at least mol % of silver chloride in a hydroquinone developer containing, as a preservative, a sulfite ion in a concentration controlled at an extremely low level, usually not more than 0.1 mol/l. Since such a developer is extremely susceptible to air oxidation due to the low sulfite concentration in the developer, various attempts have been made in order to maintain the stability of the developing activity.
In order to overcome instability in image formation according to the above-described lith development system, an image formation system is desired in which a processing solution having satisfactory preservability is used to obtain ultra-high contrast. It has been proposed to process a surface latent image type silver halide photographic material containing a specific acylhydrazine compound with a developer having a pH of from 11.0 to 12.3 and containing 0.15 mol/l or more of a sulfite preservative which exhibits satisfactory preservation stability, to form a negative image of ultra-high contrast having a gamma exceeding 10, as described in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606, 4,311,781, and 4,269,929. This image formation system has the further advantage that not only silver chlorobromide but silver iodobromide and silver chloroiodobromide can be employed, while conventional ultra-high contrast image formation systems are applicable only to silver chlorobromide having a high silver chloride content.
In general, the smaller the silver halide grains in silver halide photographic materials, the higher the blackening density obtained per unit of developed silver. In contrast, the greater the silver halide grain size, the higher the sensitivity. Therefore, achievement of both high sensitivity and high blackening density requires an increase of the content of a silver halide emulsion having a large grain size per unit area. However, a light-sensitive material having a large content of a silver halide emulsion require additional time in fixation, washing, and drying, preventing rapid processing. In addition, from the standpoint of the expensiveness of silver and limits in silver production and deposits, it is necessary to produce light-sensitive materials using a reduced amount of silver, i.e. as low as possible.
From all these considerations, studies on silver halide light-sensitive materials exhibiting high image density and high sensitivity with a reduced amount of silver have been conducted for years.
The above-described image formation system not only brings about marked improvements in sensitivity and contrast but sometimes causes an unfavorable phenomenon, called "black pepper", due to infectious development, which has presented a serious problem in the printing plate making process. The term "black pepper" as used herein means black spots of fine developed silver appearing on non-image areas (unexposed areas). Formation of black pepper frequently occurs with a decrease of sulfite ion concentration in a developer, as a preservative or an increase of the pH of the developer, resulting in considerable reduction of the commercial value of a light-sensitive material for printing plate making. Although great efforts have been made to overcome this problem, conventional techniques for eliminating black pepper are often accompanied by a reduction of sensitivity, maximum density, and gamma. Accordingly, a system free from black pepper while retaining high sensitivity and high contrast is eagerly sought.
Systems of using a chemically sensitized emulsion in combination with a hydrazine compound are disclosed in JP-A-Nos.60-83028, 61-29837, and 61-47942. They are markedly effective to obtain a high maximum density, but suffer from serious black pepper.
A combination of the compound represented by formula (I) below and a hydrazine compound was previously described in JP-A-No. 61-29837, but the disclosure does not refer to a combination with a chemically sensitized emulsion, and particularly a chemically sensitized silver iodobromide emulsion. U.S. Pat. Nos. 4,681,836 and 4,737,442 discloses hydrazine compounds. Further, U.S. Pat. No. 4,147,547 discloses the compound of formula (I) as a fog inhibitor for color silver halide photographic materials, and JP-A-Nos. 62-237445, 2-280733 and 62-280734 disclose the compound of formula (I).
Further, in the above described image formation system, a sensitizing dye added with the aim of increasing sensitivity has a remarkable influence upon gamma or black pepper appearance. JP-A-No. 61-29837 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses dyes which improve black pepper without causing reduction of gamma. These dyes, however, are attended by color remaining after development processing when used in an amount sufficient for achieving appreciable improvement of black pepper.